Tension control



Feb.

Filed June 22, 1964 TENSION CONTROL 5 Sheets-Sheet 1 7 HI lwu-w I F I IJ. y M

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S. M DOLNEY TENSION CONTROL Feb. 7, 1967 5 Sheets-$heet 4 Filed June 22,1964 m A TTO/P/VEK Feb. 7, 1967 s, DOLNEY 3,392,433?

TENSION CONTROL Filed June 22, 1964 5 Sheets-Sheet 5 I NVEN TOR.

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United States Patent 3,302,437 TENSION CONTROL Stanley M. Dolney,Pal-ma, Ohio, assignor to The Cyril Bath Company, Solon, Ohio, acorporation of Ohio Filed June 22, 1964, Ser. No. 376,751 4 Claims. (Cl.72-296) This invention relates to a prestretch fixture on a combinationof such fixtures with a draw die press, particularly to a tensioncontrol for controlling the tension applied to the stock by thestretching fixtures.

The present invention is an improvement on the structure shown in US.Letters Patent No. 3,116,780, issued January 7, 1964, Cyril J. Bath,inventor.

The object of the invention is to provide means for measuring thetension being applied to the stock during the combined stretchingoperation and drawing of the stock by closure of the dies.

Further objects and advantages will become apparent from the followingdescription wherein reference is made to the drawings, in which FIGURE 1is a front elevation of a draw die press with pre-stretch fixtures ofthe present invention installed therein;

FIG. 2 is a fragmentary top plan view of one end of the prestretchfixtures partly in section;

FIG. 3 is a vertical sectional view of the structure of FIG. 2, and istaken on the line 3-3 in FIGURES 2 and 4, part thereof being shown insection for clearness in illustration;

FIG. 4 is a horizontal sectional view of part of the structureillustrated in FIGURE 3, taken as indicated by the line 44 in FIG. 3;

FIG. 5 is a vertical sectional view of the structure illustrated in FIG.3, taken on line 5-5 thereof;

FIG. 6 is an enlarged fragmentary sectional view of part of thestructure illustrated in FIG. 5; and

FIG. 7 is a schematic hydraulic and wiring diagram showing the controlof the press and the control of the stretch heads and the relation ofthe tension control means thereto.

Referring to the drawing, the invention is shown as incorporated in aconventional hydraulic press, indicated generally at 1, comprising a bed2 with upright guide posts 3 arranged at the corners and guiding a ram 4for vertical movement toward and away from the bed. The bed 2 supports amale drawing die 5 and the ram supports a complementary female drawingdie 6. The dies 5 and 6 are conventional drawing dies which define, whenclosed, a concavo-convex pattern or patterns into which the metal isdrawn by the closure of the dies.

The ram is driven on its forming and return strokes by means of ahydraulic piston and cylinder assemblage indicated generally at 7,comprising cylinders 8 with pistons 9 therein and having piston rods 10secured to the ram. Mounted on the bed 2 is a prestretch fixture,indicated generally at 11, which comprises two units 12 arranged on thebed 2 between the post 3, one unit at each end of the male die 5. Sincethe units are the same in form and function, only one unit 12 will bedescribed in detail.

Referring particularly to FIGS. 2 through 6, each unit comprises a baseplate 13 on the ends of which are mounted guide supports 14 whichsupport upright guides 15. Each guide 15 has upright slide surfaces 16facing inwardly of the unit in a direction forwardly and rearwardly ofthe bed, and upright guide faces 17 at right angles to the surfaces 16.Mounted for vertical reciprocation in the slideways is a stretch headelevator 20 which is guided thereby for movement upwardly and downwardlywhile the elevator itself remains parallel to its starting position.

For moving the elevator 20 upwardly and downwardly, suitable piston andcylinder assemblages 21 are provided, one at each end of the elevator.Each assembladge comprises a cylinder 22 mounted in fixed position onthe sup port 14. A piston 23 is reciprocable in the cylinder and has apiston rod 24 which is connected to a plate 25 on the elevator 20. Thus,upon introduction of the hydraulic pressure fluid to the head ends ofthe assemblages 21, they move the elevator 20 upwardly, and byintroduction of the fluid to the rod end of the cylinders, they pull theelevator 2t) downwardly. These movements are under yieldable hydraulicpressure and controllable independently of the operation and control ofthe ram piston and cylinder assemblages 7.

In order to stretch the stock into -a range above its elastic limitindependently of the dies, suitable gripper heads 30 are provided, onefor each unit 11. Each head comprises an elongated body 31 which,endwise, extends forwardly and rearwardly of the press bed, and thustransversely of the direction in which the stock is to be tensioned.Each head has complementary gripping jaws 32 and 320 which arecooperable with cam surfaces 33 and 33a, respectively, so that when thejaws are moved toward the dies they grip the stock firmly. Each pair ofjaws extends substantialy the full length of the head.

In order to close its jaws, each head is provided with a plurality ofcylinders 36 in which pistons 37, having piston rods 38, arereciprocable. The rods 38 are connected by enlarged heads 39 to the jaws32 and 32a for causing them to move along the cam surfaces 33 and 33atoward and away from the dies for opening and closing the jaws. Aplurality of such piston and cylinder assemblages are provided, sixbeing employed in the form illustrated. A common manifold 41 isconnected by individual ducts 42 to the rod ends of the cylinders 36, byindividual ducts 43 through suitable connections 44 to the head ends ofthe cylinders 36. Thus all jaw operating piston and cylinder assemblagescan be operated concurrently.

As mentioned hereinbefore, it is desirable that each head 30 be arrangedso that it can move toward and away from the dies under the yieldableresistance of the hydraulic stretch forming pressure, without bindingand with a minimum or negligible amount of frictional stresses. For thispurpose, each head 30 is mounted on a carriage 50 which is mounted onthe elevator 20 for movement relative tothe elevator toward and awayfrom the adjacent ends of the dies in a horizontal path.

In order to so mount the carriage 50 on the elevator 20 whilemaintaining it under the yieldable restraint of the hydraulic stretchforming pressure, a stretch forming assemblage 52 is mounted on theelevator 20. The assemblage 52 is shown as a bank of cylinders 53. Thecylinders 53 are supported by trunnions 54 for rocking about ahorizontal axis extending lengthwise of the gripper head. The trunnions54 are rockably supported in suitable bearings 55 which are rigid withthe elevator 20.

Each cylinder 53 carries a piston 60 with a piston rod 61. The rodsextend generally horizontally and each has an eye 62 at its outer end bywhich the rod is pivotally connected by a pivot 63 to an associatedrocking link 64, three of which are used with six cylinders 53. Thelinks 64 are arranged approximately upright and at their lower ends areprovided with pivots 65. The pivots are mounted in suitable bearings 66on the elevator 20, for rocking about a common pivotal axis. Asmentioned, in the form illustrated, three links are provided for eachunit.

At their upper ends, the links 64 carry pivots 67 by which they areconnected to suit-able bearing portions on the carriage 50 for rockingrelative thereto. The pivots 63, 65 and 67, and also the trunnions 54,are horizontal and parallel to each other.

At that edge of the elevator 20 adjacent the dies, the elevator isprovided with upwardly facing horizontal trackways 70. The trackwaysextend toward and away from the dies. The carriage 50 is provided withrollers 71 which normally rest on the trackways 70, respectively.

The carriage 50 is free to rock about the axis of the pivots 67.

In addition to the foregoing structure, which is described in the aboveidentified Bath patent, an additional pair of piston and cylinderassemblages 75 are provided. Each assemblage 75 includes a cylinder 76in which is reciprocal a piston 77, having a rod 78. The rods 78 areconnected to the carriage 50 and are operable by operation of theassemblages to urge the carriage downwardly on tracks, or to rock thecarriage upwardly about the axis of the pivot 67 when such appearsdesirable in forming the stock.

Thus the assemblages 75 can control the rocked position of the carriageabout the axis of the pivot 67 above horizontal at all times.

In the Bath patent, the gripper head was mounted on the carriage infixed position relative thereto for movement with the carriage.

The structure thus far described is disclosed in the patent and does notembody the present invention.

In accordance with the present invention, and as best illustrated inFIGURE 6, the gripper head 30 is mounted on the carriage for limitedhorizontal movement relative thereto toward and away from the dies. Forthis purpose the gripper head 30 is mounted on a base 80 which, in theform illustrated, is composed of two plates 80a and 80b. The base 80 isheld in position on the carriage 50 by means of a series of bolts 81 andcarries spool keepers 82. The bolts extend through bores 83 in the base80. The spools 82 fit the bores 83 with slight radial clearance and thuspermit the base 80, and thereby the head 30, to move a small fraction ofan inch along the top of the carriage 50 toward and away from the dies.The base 80 is also connected to the carriage 50 with similar bolts 84and spools 85 arranged at the forward end to the carriage 50. Thesespools likewise permit a slight movement of the base 80 toward and awayfrom the dies along the carriage 50 and prevent the forward end of thebase from lifting upwardly relative to the carriage 50.

In order to assure that the base can move freely on the upper face ofthe carriage 50, front and rear sets 86 of recirculating roller bearingsare provided. These sets are arranged in two rows, one near the rear ofthe carriage 50 and one near the front or die side of the carriage.

Brackets 87 are mounted on the carriage 50 at the pposite end thereoffrom the gripping jaws. Brackets 88 are mounted on the gripper head 30for movement therewith and with the base 80. A tension bar 89 isconnected by pivots 90 and 91, respectively, to the brackets 87 and 88.The tension bar has a portion intermediate its ends which is thinnerthan the end portions and by which tension is measured. Sensing devices92, in the form of strain gauges, are mounted on the tension bar formeasuring the tension, which is a function of the elastic elongation ofthe bar. Two such tension bars 89 are connected to the head 30 and arearranged at opposite sides of the center line of the head, eachpreferably midway between the nearest end of the head, forwardly andrearwardly of the press, and the centerline of the head.

Generally the heaviest tension is applied by the head 30 at thebeginning of the operation while the head holds the sheet in horizontalposition between and clear of the dies. In such position the smallfraction of an inch which the gripper head 30 moves relative to thecarriage 50 is horizontal and free from any substantial friction,because the longitudinal axis of the tension bar, indicated at xx is ata level between the gripping faces of the jaws. Accordingly, the tensionbar can reflect the actual tension applied to the stock. On the otherhand, if the stock should slope upwardly from the gripping jaws in adirection toward the dies as the elevator is being lowered duringforming the stock around one end of the die, the entire carriage 50swings upwardly about the pivot 67 so that the tension applied by thehead 30 on the bar 89 is still parallel to the upper surface of thesupport and parallel to the axis xx of the tension bars. Consequently,the tension is accurately reflected by the strain gauges. The weight ofthe base 80 and the gripping head 30 carried thereon can affect theresult very slightly and usually this is not sufficient to be seriousexcept when very great downward components are necessary for wrappingthe stock around one end of the male die. Even in such cases, thiseffect can be offset by actuating the assemblages 75 for the properinclining of the carriage in the direction of tension and the directline pull on the stock.

In order to assure that the elevator 20 retains the same level at bothends, a suitable shaft 94 is mounted on the machine frame and carriesgears 95 at its ends. The gears 95 are in mesh with racks 96 on theopposite ends of the elevator, so that the shaft 94 is constrained torotate the same at both ends, thus assuring that the elevator rises andfalls the same distance at each end.

Referring next to FIGURE 7, the strain gauges 92 are connected to anamplifier 97, which in turn is connected across the power source L1-L2.The amplifier 97 operates a control 98 which controls a reversibleelectric motor '99. The motor drives an adjustable pressure relief valve100 according to the setting of the control 98, and thus controls thepressure in the stretch assemblies in accordance with the elasticelongation of the tension bar.

The terms Upright and horizontal where used herein and in the claims areused in a relative sense for briefness in defining relative positionsand movement of various parts, and not as absolutes. The valve 100 isoperated to increase the pressure to the stretching assemblage forstretching when the tension is below a predetermined amount, and toreduce the pressure when the tension rises above a predetermined amount.Valve 100 is in the pressure feed line at the reversing and stop valveof the stretch assemblies 52. Thus the tension applied by the stretchassemblages is regulated by the tension bar 89 acting through the straingauges 92.

If desired, a strain gauge 101 may be provided on the tension bar 89 andconnected through the amplifier 97 to a voltmeter 102 calibrated intotal stretch forming tension applied to the bar 89. The strain gaugesmay be such as disclosed in US. Letters Patent No. 2,292,549, issuedAugust 11, 1942. The circuitry for use of signals from such straingauges is well known and is here shown broadly diagrammatically. A moredetailed description may be found in US. Letters Patent No. 2,849,048,issued August 26, 1958. The important feature of the present inventionis the combining of the tension bars with stretch units of astretch-draw press.

Referring to FIG. 7, the ram piston and cylinder assemblages may besupplied with pressure fluid from a pump 104, driven by a motor 105,through a solenoid operated, spring restored, cutoff and reversing valve106.

The other piston and cylinder assemblages may be supplied by a pump 107driven by a motor 108. The supply to the elevator assemblages 21 isthrough a spring return solenoid operated cutoff and reversing valve109, and that to the gripper cylinder 36 through a like valve 110, Thesupply to the stretch forming assemblage 52 is through a solenoidoperated spring return cutoff reversing valve The relief valve 100, forcontrolling the applied tension is connected between the pump and valve111. Pressure fluid is supplied to the assemblages 75 from the pump 107through a spring return reversible cutofl? valve 112.

A flow regulator 113, controlled by a motor 114, is interposed betweenthe pump 107 and the valve 199, as also is a pressure regulator 115driven by a motor 116.

correspondingly, a flow regulator 117 driven by a motor 118, and apressure regulator 119 driven by a motor 120 are interposed between thepump 107 and valve 112.

The stretch units being duplicates, like circuits are provided for each.

It is apparent from the foregoing description that the enefits of thedesired movements and operation of the stretch heads 30 can bemaintained while obtaining a signal which reflects the actual tension onthe sheet, regardless of any frictional forces in the power mechanisms,carriage 50, and elevator 29. Such forces can affect the tension on thesheet and such tension is the algebraic resultant of all forces actingin the tensioning direction and this alone is reflected by the tensionbars 89.

The movement of the base 80 relative to the carriage 50 is very slightwith the friction free connection described and the direct tension islengthwise of the bar at all times. Consequently no appreciablefrictional forces are introduced between the sheet and tension bar.

The various flow controls, relief valves, and pressure controls canreadily be adjusted and coordinated and remotely controlledautomatically by control of their motors in response to the signals fromthe tension bars 89.

Having thus described my invention, I claim:

1. A prestretch fixture comprising a frame, a stretch head including ajaw for gripping the margin of a length of metal to be stretched, acarriage for the head, means supporting the carriage for movement inopposite directions in generally upright paths and for movement,concurrently with the movement in said generally upright paths, inopposite directions in generally horizontal paths in all positions ofthe carriage along said upright path, power means operable to cause saidconcurrent movements of the carriage, means connecting the head to thecarriage for substantially free movement of the head relative to thecarriage in said opposite directions in said generally horizontal paths,said power means including stretch forming power means yieldably urgingthe carriage in one of said directions in said generally horizontalpath, and stress measuring tension =bar means interconnecting thecarriage and head and extending in said one direction from the head tothe carriage and operative for restraining said movement of the headrelative to the carriage and for concurrently transmitting between thehead and carriage the tensioning forces imposed by the stretch formingpower means.

2. An apparatus according to claim 1 wherein the head and the carriageare elongated horizontally transversely to the direction of movement ofthe head for applying tension, and the stress measuring tension barmeans comprise a plurality of tension bars spaced from each otherlaterally lengthwise of the head and carriage, and each barinterconnecting the carriage and head.

3. An apparatus according to claim 1 wherein the carriage is connectedto the supporting means for swinging upwardly about a horizontal axisduring movements of the carriage along said generally horizontal andupright paths, and supplemental power operable means are provided andinterconnect the supporting means and carriage and are operable forswinging the carriage about said horizontal axis during said movements.

4. An apparatus according to claim 3 wherein means are provided to lockthe supplemental power operable means for holding the carriage indifferent swing positions, selectively.

References Cited by the Examiner UNlT ED STATES PATENTS 2,974,708 3/1961Perkins 7220 3,113,607 12/1963 Maize 72-296 3,116,780 1/1964 Bath a72297 CHARLES \V. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner.

1. A PRESTRETCH FIXTURE COMPRISING A FRAME, A STRETCH HEAD INCLUDING AJAW FOR GRIPPING THE MARGIN OF A LENGTH OF METAL TO BE STRETCHED, ACARRIAGE FOR THE HEAD, MEANS SUPPORTING THE CARRIAGE FOR MOVEMENT INOPPOSITE DIRECTIONS IN GENERALLY UPRIGHT PATHS AND FOR MOVEMENT,CONCURRENTLY WITH THE MOVEMENT IN SAID GENERALLY UPRIGHT PATHS, INOPPOSITE DIRECTIONS IN GENERALLY HORIZONTAL PATHS IN ALL POSITIONS OFTHE CARRIAGE ALONG SAID UPRIGHT PATH, POWER MEANS OPERABLE TO CAUSE SAIDCONCURRENT MOVEMENTS OF THE CARRIAGE, MEANS CONNECTING THE HEAD TO THECARRIAGE FOR SUBSTANTIALLY FREE MOVEMENT OF THE HEAD RELATIVE TO THECARRIAGE IN SAID OPPOSITE DIRECTIONS IN SAID GENERALLY HORIZONTAL PATHS,SAID POWER MEANS INCLUDING STRETCH FORMING POWER MEANS YIELDABLY URGINGTHE CARRIAGE IN ONE OF SAID DIRECTIONS IN SAID GENERALLY HORIZONTALPATH, AND STRESS MEASURING TENSION BAR MEANS INTERCONNECTING THECARRIAGE AND HEAD AND EXTENDING IN SAID ONE DIRECTION FROM THE HEAD TOTHE CARRIAGE AND OPERATIVE FOR RESTRAINING SAID MOVEMENT OF THE HEADRELATIVE TO THE CARRIAGE AND FOR CONCURRENTLY TRANSMITTING BETWEEN THEHEAD AND CARRIAGE THE TENSIONING FORCES IMPOSED BY THE STRETCH FORMINGPOWER MEANS.